content: /*
   * Copyright 2016-present David Karnok
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package hu.akarnokd.rxjava3.operators;
  
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.*;
  
  import org.reactivestreams.*;
  
  import io.reactivex.rxjava3.core.*;
  import io.reactivex.rxjava3.disposables.Disposable;
  import io.reactivex.rxjava3.exceptions.MissingBackpressureException;
  import io.reactivex.rxjava3.internal.disposables.DisposableHelper;
  import io.reactivex.rxjava3.internal.subscriptions.SubscriptionHelper;
  import io.reactivex.rxjava3.internal.util.BackpressureHelper;
  import io.reactivex.rxjava3.plugins.RxJavaPlugins;
  
  /**
   * Issues {@link Subscription#request(long)}(1) after the initial delay and then at each period.
   *
   * @param <T> the item type
   * @since 0.18.6
   */
  final class FlowableRequestSampleTime<T> extends Flowable<T> implements FlowableTransformer<T, T> {
  
      final Flowable<T> source;
  
      final long initialDelay;
  
      final long period;
  
      final TimeUnit unit;
  
      final Scheduler scheduler;
  
      FlowableRequestSampleTime(Flowable<T> source, long initialDelay,
              long period, TimeUnit unit, Scheduler scheduler) {
          super();
          this.source = source;
          this.initialDelay = initialDelay;
          this.period = period;
          this.unit = unit;
          this.scheduler = scheduler;
      }
  
      @Override
      public Publisher<T> apply(Flowable<T> upstream) {
          return new FlowableRequestSampleTime<>(upstream, initialDelay, period, unit, scheduler);
      }
  
      @Override
      protected void subscribeActual(Subscriber<? super T> s) {
          RequestSample<T> parent = new RequestSample<>(s);
          s.onSubscribe(parent);
          DisposableHelper.setOnce(parent.timer, scheduler.schedulePeriodicallyDirect(parent, initialDelay, period, unit));
          source.subscribe(parent);
      }
  
      static final class RequestSample<T>
      implements FlowableSubscriber<T>, Subscription, Runnable {
  
          final Subscriber<? super T> downstream;
  
          final AtomicLong downstreamRequests;
  
          final AtomicLong upstreamRequests;
  
          final AtomicReference<Subscription> upstream;
  
          final AtomicReference<Disposable> timer;
  
          long emitted;
  
          boolean done;
  
          RequestSample(Subscriber<? super T> downstream) {
              this.downstream = downstream;
              this.downstreamRequests = new AtomicLong();
              this.upstreamRequests = new AtomicLong();
              this.upstream = new AtomicReference<>();
              this.timer = new AtomicReference<>();
          }
  
          @Override
          public void onSubscribe(Subscription s) {
              SubscriptionHelper.deferredSetOnce(upstream, upstreamRequests, s);
          }
  
          @Override
          public void onNext(T t) {
              if (!done) {
                  long e = emitted;
                  if (downstreamRequests.get() != e) {
                      emitted = e + 1;
                      downstream.onNext(t);
                  } else {
                      done = true;
                      cancel();
                      downstream.onError(new MissingBackpressureException("Downstream is not ready to receive the next upstream item."));
                  }
              }
          }
  
          @Override
          public void onError(Throwable t) {
              if (!done) {
                  done = true;
                  downstream.onError(t);
                  DisposableHelper.dispose(timer);
              } else {
                  RxJavaPlugins.onError(t);
              }
          }
  
          @Override
          public void onComplete() {
              if (!done) {
                  done = true;
                  downstream.onComplete();
                  DisposableHelper.dispose(timer);
              }
          }
  
          @Override
          public void run() {
              SubscriptionHelper.deferredRequest(upstream, upstreamRequests, 1);
          }
  
          @Override
          public void request(long n) {
              BackpressureHelper.add(downstreamRequests, n);
          }
  
          @Override
          public void cancel() {
              SubscriptionHelper.cancel(upstream);
              DisposableHelper.dispose(timer);
          }
      }
  }
  